Commutator for a small electrodynamic machine

ABSTRACT

A commutator for a small electric motor wherein the commutator segments are made by stamping same from a metal strip or a metal sheet provided with a contact layer which consists of an alloy of noble metals rolled on to the substrate metal. In a preferred embodiment, the alloy comprises 70 + OR - 1 percent of gold, 20 + OR - 1 percent of silver, 10 + OR - 1 percent of copper, and an impurity content in the form of other metals which is at most 0.05 percent.

United States Patent 91 van de Griend [111 3,805,103 [451 Apr. 16, 1974 COMMUTATOR FOR A SMALL ELECTRODYNAMIC MACHINE Inventor:- Jan Maarten van de Griend,

Dordrecht, Netherlands Assignee: U.S. Philips Corporation, New

York, NY.

Filed: Sept. 13, 1971 Appl. No.: 179,774

Foreign Application Priority Data Sept. 18, 1970 Netherlands 7013888 US. Cl 310/237, 29/199, 117/230 Int. Cl. H02k 13/04 Field of Search 310/44, 45, 233, 235, 236, 310/237, 228, 231; 252/514; 29/199; 117/230, 130, 130 E References Cited UNITED STATES PATENTS 9/1967 Brinster 310/233 3,617,785 11/1971 Kristiansen 310/236 3,347,799 10/1967 Wagner 252/514 3,468,676 9/1969 Schneble 177/130 E 3,014,144 12/1961 Fleishmann.... 310/237 3,414,970 12/1968 Yamaguchi.... 310/237- 3,478,421 11/1969 Preece 310/237 3,005,920 10/1961 Dolzau 310/235 Primary Examiner-R. Skudy Attorney, Agent, or Firm-Frank R. Trifari [5 7] ABSTRACT A commutator for a small electric motor wherein the commutator segments are made by stamping same from a metal strip or a metal sheet provided with a contact layer which consists of an alloy of noble metals rolled on to the substrate metal. In a preferred embodiment, the alloy comprises 70 i 1 percent of gold, 20 i 1 percent of silver, 10 i 1 percent of copper, and an impurity content in the form of other metals which is at most 0.05 percent.

5 Claims, 1 Drawing Figure PATENTEUIPHBBH 11805303 INVENTOR.

JAN MAARTEN VAN DE GRIEND K Agent silver palladium alloy.

COMMUTATOR FOR A SMALL ELECTRODYNAMIC MACHINE This invention relates to a commutator for a small electrodynamic machine in which the commutator segments are made of sheet material which is composed of a metal substrate and a contact layer which consists of an alloy of noble metals which is rolled on to the substrate.

Different embodiments of such commutators are known. Especially manufacturers in the German Federal Republic frequently use such commutators in small direct-current motors, the contact layer consisting of a ""xarsaavairiag'ebfifiiaiib'i is its comparatively limited useful life which, even under favourable conditions, may typically be about 1,000 hours. Furthermore, owing to the comparatively rapid formation of wear particles, the quality of the commutation is not such as to render these alloys suitable for use in electronically controlled small direct-current motors of the type used in battery-fed music reproducing apparatus. Since the electronic control requires a highly constant contact resistance between the commutator segments and the brushes, the latter always are made of metal in commutators of this type.

A far better commutation quality is obtainable with commutators as frequently used in particular in Anglo- Saxon countries, which commutators are provided with a layer of a gold alloy by clectrodeposition. In addition, these commutators may reach lifetimes of about 1,500 hours.

However, in many cases a longer useful life is desirable. Besides, the questions of useful life and commutation quality cannot be separately considered when an electronic control is used, for the products of wear readily impair the contact between the brushes and the commutator and hence give rise to a variation of the effective contact resistance between the brushes and the commutator segments and to short-circuits between the segments, resulting in unreliability of the speed control.

Manufacture of a commutator provided with a layer of a gold alloy by clectrodeposition is comparatively complicated and, if satisfactory results are to be achieved, requires about thirty different baths. Moreover, the compositionof some of these baths is highly critical so that it is very difficult to maintain a high quality for a prolonged period of time. Obviously, installation and operation of so high a number of electrodeposition baths having sizes suitable for mass production requires considerable amounts of money.

Notwithstanding the described grave disadvantages,

' to which further ones might be added, the manufacturers of small high-quality electric motors suitable for use in advanced-technology apparatus, such as portable cassette recorders, Hi-F i record players, etc., have opted for flat commutators provided with electrodeposited noble-metal alloys because the qualities of such commutators have been unsurpassable sofar.

However, the invention provides a commutator of the type defined at the beginning of this specification which in respect of useful life and quality of commutation is considerably better and moreover has the advantage of the said commutators, i.e., greater ease in automation of manufacture, the commutator according to the invention being characterized in that the said contact layer consists of a gold alloy. The novel commutator is especially useful in the commutator structure disclosed in my copending U.S. application, Ser. No. 180,027, filed Sept. 13, 1971.

One form of the invention will now be described with reference to the sole FIGURE of the accompanying drawing.

In the FIGURE, a flat commutator 1 is composed of segments 2 mounted on a metal substrate 3 and separated by insulation strips 5. The commutator is mounted for rotation about a shaft 4. Each segment is made of a gold alloy to be described below.

In an embodiment of the invention which has proved highly suitable for the intended use, the gold alloy comprises i 1 percent of gold, 20 i 1 percent of silver, the remainder being copper and impurities.

Very good results are obtainable by means of a further embodiment which is characterized in that the gold alloy contains 10 i 1 percent of copper.

A preferred embodiment is characterized in that the percentage of impurities in the alloy which takes the form of metals which do not belong to the group gold, silver and copper is at most 0.05 percent.

Important with respect to the useful life is a further embodiment which is characterized in that the mean roughness of the surface of the contact layer is at most 2 ru, i.e., two times unity surface roughness ru. The value of this unit is expressed in ,u. or in microinches, wherein 1 LL 40 micro-inches.

Investigations have shown that flat commutators provided with a contact layer according to the two latter embodiments may reach a lifetime of more than 5,000 hours while retaining a hitherto unknown commutation quality. In addition it has been found that manufacture of such commutators with the use of known mass production methods is so much simpler that ultimately their cost is lower than that of the aforementioned commutators having electrodeposited contact layers.

What is claimed is:

l. A commutator for a small dynamo-electric machine comprising, a plurality of commutator segments made of a sheet material wherein each segment comprises a metal substrate and a contact layer on the substrate, and said contact layer comprises a gold alloy of noble metals containing 70 i 1 percent of gold, 20 :L 1 percent of silver, the remainder being composed of copper and impurities.

2. A commutator as claimed in claim 1, characterized in that the gold alloy contains 10 i 1 percent of copper.

3. A commutator as claimed in claim 2, characterized in that the percentage of impurities in the alloy include at most 0.05 percent of metals other than gold, silver and copper.

4. A commutator as claimed in claim 3, characterized in that the mean roughness of the surface of the contact layer is at most 2 ru.

5. A commutator for a small dynamo-electric machine comprising, a plurality of flat commutator segments insulated from one another, said segments being formed of a metal substrate covered by a contact layer, and said contact layer comprises an alloy containing 70 i 1 percent gold, 20 i 1 percent silver with the remainder composed of copper and other metal impurities. 

2. A commutator as claimed in claim 1, characterized in that the gold alloy contains 10 + or - 1 percent of copper.
 3. A commutator as claimed in claim 2, characterized in that the percentage of impurities in the alloy include at most 0.05 percent of metals other than gold, silver and copper.
 4. A commutator as claimed in claim 3, characterized in that the mean roughness of the surface of the contact layer is at most 2 ru.
 5. A commutator for a small dynamo-electric machine comprising, a plurality of flat commutator segments insulated from one another, said segments being formed of a metal substrate covered by a contact layer, and said contact layer comprises an alloy containing 70 + or - 1 percent gold, 20 + or - 1 percent silver with the remainder composed of copper and other metal impurities. 